Unhexseptium
Unhexseptium, Uhs, is the temporary name of element 167. Properties NUCLEAR At least one set of theoretical values for half-lives and decay modes of Uhs have been constructed for neutron count up to N = 333(1). It predicts isotopes in a band ranging from Uhs 454 to Uhs 484. Examination of pp 15 & 18 of Ref. 1 indicates that Uhs 454 through Uhs 457 are predicted to decay by fission and have sub-microsecond half-lives. Uhs 458 to Uhs 475 decay by alpha emission with half-lives increasing with A and peaking at 0.001 – 1 sec in the Uhs 469 to Uhs 475 range. Heavier isotopes also decay by alpha emission, but have short halflives. These predictions are to be expected for neutron shell closure at N = 308. Ref. 1 also shows a predicted isotope at Uhs 499, which is probably an artifact. What Ref. 1 can’t do is describe heavy isotopes of Uhs. It is possible to use a first-order, liquid-drop approach to guess at the amount of structural correction energy needed to allow a drop of nuclear matter to survive for the 10^-14 sec needed for electromagnetic interactions (such as binding an electron) to become important. At least two computations of the neutron dripline’s location up to Z = 175 exist(2),(3), and since they give similar results, the maximum possible size of a Uhs nucleus can be set slightly above the values computed, allowing only a small margin for error. This gives Uhs 597 as the heaviest possible Uhs isotope. Structural correction required for Uhs 597 itself is around 0.75 MeV, which means all Uhs drops will fission quickly without structural stabilization. In general, it is not possible to describe structural correction energy. What can be predicted are neutron and proton shell closures, for which correction energy is expected to be particularly large. Neutron shell closures have been predicted at N = 406(3),(4), 370(3), 318(5), and 308(1). The isotope Uhs 573 requires a little less than 1.5 MeV of structural correction, which means isotopes in the Uhs 563 to Uhs 578 band are likely. (See “Formation” for additional significance of these nuclei.) Uhs 537 requires around 1.5 MeV of structural correction, which means isotopes in the band Uhs 527 to Uhs 542 are also likely. All isotopes in both bands should beta-decay with half-lives under a second. On the other hand, Uhs 485 requires around 3 MeV of correction energy, which means alpha-decaying nuclei are likely in the band Uhs 475 to Uhs 490. Ref. 1 does not show a pattern of nuclides which indicate a shell closure at N = 318. Uhs 475 requires 3.5 MeV of correction energy, which is realistic for a strong neutron shell closure, such as the one predicted at N = 308, so the liquid-drop picture isn’t unrealistic. ATOMIC Several predictions for the ground state electron structure of Uhs agree that it will have p-block character, with two 9s electrons and a 9p1/2 electron available for bonding. Electrons in Uhs can be described in terms of time-independent orbitals, but calculation of electron properties require that nuclear charge be distributed over the nucleus' actual volume. In addition, there is some chance that differing nuclear shapes may produce different electron configurations in different isotopes. (Different isotopes would be different elements in the chemical sense.) Except in the laboratory, Uhs is expected to exist only in environments too hot for ordinary chemistry to occur. FORMATION Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. There is a possibility that beta decay from dripline nuclides stabilized by the N = 406 closure, enhanced by the Z = 164 proton shell closure, will allow some isotopes in the vicinity of Uhs 563 to Uhs 577 to form in quantity during such a merger. It improbable that nuclides between Uhs 527 and Uhs 542, or lighter, can form in this way. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Uhs 454 to Uhs 484 band. Quantities produced by this method are very small. References 1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 2. "Neutron and Proton Drip Lines Using the Modified Bethe-Weizsacker Mass Formula; D.N. Basu et al; Int.J.Mod.Phys.; arXiv:nucl-th/0306061; url: https://arxiv.org/abs/nucl-th/0306061 3. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 4. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 5. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (12-12-19) References Category:Undiscovered elements Category:Halogens Category:Radioactive